Seat back



FIG. 1 is a perspective view of a seat back showing my new design;

FIG. 2 is another perspective view thereof;

FIG. 3 is a front elevational view thereof

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof;

FIG. 6 is a right side elevational view thereof;

FIG. 7 is a top plan view thereof; and,

FIG. 8 is a bottom plan view thereof.

The broken lines in the drawings depict portions of the seat back thatform no part of the claimed design.

CLAIM The ornamental design for a seat back, as shown and described.